Field
Implementations described herein generally relate to zeolite compositions and organic-free methods for forming such zeolites
Description of the Related Art
The global synthetic zeolite industry accounts for approximately $1.9 billion in revenue annually. The unique acidity, thermal stability, and shape-selectivity of nanoporous zeolites are beneficial for industrial applications such as catalysis. Zeolites are commonly used as catalysts in petroleum refining and chemicals production, and are highly active in the selective catalytic reduction of diesel and lean-burn vehicle emissions. Moreover, zeolites are commonly used for ion-exchange and are promising materials for selective separations. Research in both industry and academia seeks to design more rational synthetic approaches capable of improving zeolite properties for existing petrochemical processes, for emerging applications (such as NOx reduction in diesel emission), and for research objectives aimed to expand zeolite application to non-conventional markets, such as sensor technologies, drug delivery, and enantioselective catalysis and separations.
Among the 200 unique zeolite framework types, only a small percentage of structures are heavily utilized in commercial applications. One of the major economic factors in commercial zeolite synthesis is the use of organic structure-directing agents (SDAs), which are molecules possessing a size and shape commensurate with zeolite pores and channels. SDAs alter the kinetics of zeolite crystallization and guide the formation of the crystalline framework structure; however, the organic SDA becomes occluded within the pores and must be removed by a post-treatment calcinations process wherein the SDA is decomposed, which prevents the possibility of recycling (i.e., a high economic cost considering the price of the organics). As such, commercial processes rely on organic-free (often termed template-free) syntheses. The economic advantage of this approach is evident; however, there are two critical challenges that must be overcome: (i) there are only a handful of known zeolite crystal structures that can be synthesized in the absence of organic SDAs, and (ii) syntheses often result in the formation of two or more structures (i.e., crystal polymorphs or structures of similar composition). It is therefore desirable to establish synthesis conditions for zeolite growth that ensures the formation of a single (pure) crystal phase. To this end, the implementations disclosed herein provide growth conditions that lead to the formation of seven different zeolite framework structures, each in a pure crystal phase without any impurities.